Holder for use in repointing twist drills



Dec. 19; 1944.

D. CRQWTHER HOLDER FOR USE IN RE-POINTINQ TWIST DRILLS Filed Oct. 30, 1943 D [NVENTOB BY WW /1 ATTORNEY metrically opposite each other.

the extreme end of the drill is formed by the in- Patented Dec. 19, 1944 HOLDER FOR USE IN REPOINTING -TW'IST1DR1LLS David Crowther, Minneapolis. Minn.

=Applicationctober 30, 1943, :Serial No.-508,432

4 Claims.

My invention relates to holders for use in repointingtwist drills. It relates moreparticularly to a device to be held in the hand of the operator with the drill which is to be re-pointed clamped in the device in order to grind'the cutting end of the drill at the most desirable and eificient angles and without the device having any"attachment 'Whateverto a grinding machine. An object therefore is to provide a device of this character'which is simple and inexpensive to manufactureand at the same time is efficient and convenient for holdmg thedrill so that it may be properly brought into engagement with a grinding wheel for-accurately sharpening a dull 'drill.

In the metal drilling art,-a twist drill has a body portion provided with a -point," the latter being the entire cutting end. sp'iral grooves known asfiutes extend along the Two deeply "cut sides of the body member, these grooves being dia- A sharp tip at tersection of'the flutes and the cutting edges or lips and this tip must be kept in the exact center of the axis of the 'drill. The heel is the por- 'tion ofthe "point back of the cutting lips. An efficient cutting edge for'the lips would not be provided unless they are sharp. So in orderto give this cutting edge, the surface of the point" must be ground exactly back of the lips, this being known as lip clearance. This clearance allows the lips to enter the metal which is being drilled and the effectiveness of the drill depends largely on the grinding of the lip clearance at the proper :angle which is 12 at the periphery of the drill.

Furthermore, the most desirable angle which is given to the cutting lips'is considered to be 29 /2" with relation to th axis. With the foregoin exmeans of which the angles just referred to may be readily and accurately ground in order to properly re-point the drill.

The novel features which I believe characteristic of my invention are set forth With particularity in the appended claims. The invention, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of a specific embodiment thereof when it is read in connection with the accompanying drawing in which,

Fig. 1 is a sectional view showing the point of a drill in proximity to a grinding wheel.

Fig. 2 is a view of the devicev taken on the line :c-a: Fig. 1.

Fig. 3 is aside elevationalview'ofasIightmodL 'fication.

Fig. 4 is acrosssectional view of the block used.

i Referring-to the constructionshown in them:- companying drawing in order to illustrate the principle involved in this invention, the numeral -l designates 'a cone-shaped membergof wear. re- 'sistant material suchas carborundum having an axial bolt Zsecured thereto andprojecting from the larger end of the member I.

This projecting end portion is screwthreaded. "A block 3 is provided with one or more longitudina1 V shaped grooves l, land with a hole 5 for receiving the bolt 2. A hollowed-out clamping nut Bcontaining a coiled spring 'I'is threaded on the sc'rew threaded portion of the bolt 2 in order thata drill D may be firmlyheld in'the groove between member I.

vided, this member containinga set screw 9 which the block 3 and the 'largerend of the member I.

As shown, the hole 5 in the block 3 is so located that the forward end of this block projects slightly beyond the periphery'oithe larger end of the A stop member 8 is preferably prowhen turned down clamps the member ll to the body portion of the'drill. This stop assists in keeping'the drill in the same longitudinal position in the groove 4 when the drill is turned exactly half way around therein in order to grind the opposite side of the point exactly the same "as the side already ground.

- The operationand advantages of my invention will be readily understood in connection withthe foregoing description and the accompanyin drawing. In order to re-point a drill when it becomes dull, the drill is placed in the groove at the right hand portion of the block 3 with the point of thedrillextending beyond the rear end of the block the proper amount to be ground away as determined by the position of the stop mem- "ber 8. The device is held in the hand of the operator and. brought into proximity with the surface of a grinding wheel G until the point" of the drill is ground down as much as the cone member I will permit when it comes into contact with the grinder. The device holding the drill is given a slight back and forth rotative movement with the point in engagement with the grinding wheel and the heel is ground away to turned half way around in the groove, the stop member 8 when provided assisting to make sure that the drill is properly positioned in the groove. The grinding process just described is then repeated so that the other side of the point is ground exactly the same as the first side.

In regard to obtaining the proper angle for the lip clearance of the heels back of the lips, it should be recalled that if two parallel straight lines are drawn across a circle not going through the center thereof, the angles which the lines make at the periphery of the circle will vary according to the distance which they are from the center of the circle. This principle i made use of in obtaining the desired angle for the lip clearance. The two lines may be considered as representing the two opposite sides of the drill in the groove and the circle is the periphery' of the larger end of the cone-shaped member. I.

Therefore by placing the V groove the proper distance from the center of said larger end, the desired angle for lip clearance will be obtained. It will be understood as a matter of course that the two lines may be varied in accordance with the size of the drill and that different blocks may be provided in accordance with thickness of the drills. Fig. 2 shows a second groove 4' which is diagonally opposite the groove 4 so as to be on the other side of the axis of the member I and it is at a slightly different distance therefrom., In case the cone member I in time should wear down slightly, this groove may then be used in .which to hold the drill. The groove 4' also provides for receiving a drill of different size.

I have already indicated that more than one groove may be made in the block 3 and that the groove which is used must be on the right hand 7 l3, and M in Fig. 4. The block I0 is provided with two holes 5 and 5 at right angles to each other. Fig. 3 shows the position of the lips of the drill with respect to the holder and the grinding wheel.

I claim:

1. A holder for use in re-pointing twist drills comprising a cone-shaped member of wear resistant material, a block containing at least one longitudinal groove, and means for clamping the drill in the groove between the block and the larger end of the cone-shaped member in such position that when the drill is placed adjacent to a grinding device the cutting lips of the drill may be ground down to the angle of inclination of the cone-shaped member and the distance of said groove from the axis of the cone-shaped member being such that the heel portions of the drill may be ground down at an angle determined by said distance.

2. A holder for use in re-pointing twist drills comprising a cone-shaped member of wear resistant material, an axial bolt secured to said member and projecting from the larger end thereof with the projecting portion screw threaded, a block containing at least one longitudinal groove and having a hole into which said bolt is inserted, and a'clamping nut threaded upon said projecting portion for holding the drill in the groove between the block and the larger end of the cone-shaped member in such position that ,when the drill is placed adjacent to a grinding device the cutting lips of the drill may be ground down to the angle of inclination of the coneshaped member and the distance of said groove from the axis of the cone-shaped member being such that the heel portions of the'drill may be ground down at an angle determined by said distance.

3. A holder for use in re-pointing twist drills comprising a cone-shaped member of wear resistant material, a block containing two longitudinal grooves on opposite faces thereof and at different distances from the axis of said coneshaped member, and means for clamping the drill in either one of said grooves between the block and the larger end of the cone-shaped member in such position that when the drill is placed adjacent to a grinding device the cutting lips of the drill may be ground down to the angle of inclination of the cone-shaped member and the distance of said grooves from the axis of the cone-shaped member being such that the heel portions of the rill may be ground down at an angle determined by said distance.

4. A holder for use in re-pointing twist drills comprising a cone-shaped member of Wear resistant material, a block containing at least one longitudinal groove, means for clamping the drill in the groove between the block and the larger end of the cone-shaped member, and a stop member adapted to be clamped on the bod portion of the drill in such position that the engagement of the stop member with the front end of the block will determine the desired projection of the point of the drill beyond the cone-shaped member in such position that when the drill is placed adjacent to a grinding device the cutting lips of the drill may be ground down to the angle of inclination of the cone-shaped member and the distance of said groove from the axis of the coneshaped member being such that the heel portions of the drill may be ground down at an angle determined by said distance.

DAVID CROWTHER. 

